Molded plastic parts are widely used in automobiles, trucks, household appliances, graphic arts and the like. Frequently these plastic parts are made from polyolefins such as polyethylene, ethylene copolymers, polypropylene, propylene copolymers and polyolefin blends with other polymers. One such blend is a thermoplastic polyolefin (TPO), which is a rubber-modified polypropylene. Frequently, these plastic parts have to be painted to match the color of painted metal parts that are also present in the automobile, appliance or other items. Typical paints do not adhere well to these plastic parts. Thus, adhesion-promoting primers are needed to improve the adhesion of the paints to the polyolefin materials.
Chlorinated polyolefins, particularly chlorinated, maleated crystalline polypropylene polymers are effective as adhesion-promoting primers and they have very limited solubility in anything other than aromatic or chlorinated solvents. The U.S. Federal Clean Air Act of 1990 limits the amounts of solvents that are on the Hazardous Air Pollutants (HAPs) list that can be used in some areas, and most practical aromatic and chlorinated solvents for use in coatings applications are on the HAPs list. There are some applications where a non-chlorinated adhesion promoter is desired. Other systems proposed for use as primers are based on maleated amorphous polyolefins, which are dissolved in aromatic solvents such as xylene and toluene.
Attempts have been made to provide water based paints and primers for the automotive and appliance industries but these systems generally are not thought to be as effective as solvent based systems. For example, the polymers used in water based systems must be emulsified or dispersed in water using a nonionic, cationic or anionic surfactant and a primary, secondary or tertiary amine, which can lend water-sensitivity to the applied coating.
U.S. Pat. No. 4,286,047 describes pressure-sensitive adhesives that are readily detackifiable by exposure to ultraviolet radiation. These adhesive systems contain a normally tacky and pressure-sensitive adhesive having an epoxy equivalent value of about 400-900 and including an effective amount of an ionic photoinitiator. These adhesives show a decrease in adhesion to surfaces such as glass, aluminum, circuit boards, silicon wafers, and enamel after exposure to ultraviolet radiation.
U.S. Pat. No. 4,303,697 discloses a process for improving the adhesion of paint to polyolefin surfaces. In this process polyolefin surfaces, such as polyethylene, polypropylene, ethylene/propylene copolymers, and EPDM copolymers (TPOs), are primed with a chlorinated polyolefin, which comprises chlorinated polypropylene and chlorinated polypropylene containing carboxylic anhydride groups, and then exposed to ultraviolet radiation. This treatment improves both the dry and wet adhesion of paint to the polyolefin surfaces.
U.S. Pat. No. 4,880,849 describes a coating composition which crosslinks upon exposure to ultraviolet radiation. This composition consists of (a) from 1 to 5 percent of a saturated, chlorinated polymeric material selected from the group consisting of (1) a chlorinated polyolefin containing about 5 to 75 percent by weight of chlorine and having a number average molecular weight of about 5,000 to 50,000, (2) a chlorinated polyolefin containing carboxylic anhydride groups and about 5 to 25 percent by weight of chlorine and having a number average molecular weight of about 5,000 to 50,000, and (3) a mixture thereof; (b) from 20 to 80 percent of a radiation sensitive monomer having at least two addition polymerizable unsaturated bonds; (c) from 0.1 to 5.0 percent of a photopolymerization initiator; and (d) from 80 to 20 percent of an acrylic addition polymer having at least one amino group and having a number average molecular weight of about 8,000 to 70,000. This patent discloses a method of coating comprising (1) applying a film of the coating composition of the invention to a plastic substrate, and (2) curing the film by exposing the film to ultraviolet radiation.
U.S. Pat. No. 4,968,559 describes an adhesive film comprising (a) a base film permeable to ultraviolet light, (b) a layer of a pressure sensitive adhesive formed on one side of the film.
U.S. Pat. No. 5,118,567 describes an adhesive tape comprising an energy beam transmittable base sheet and an adhesive layer formed on the surface of the said base sheet.
U.S. Pat. No. 5,373,048 discloses a composition for a water based adhesion promoter that consists of a non-chlorinated polyolefin, a nonionic surfactant, a primary, secondary or tertiary amine, and water.
U.S. Pat. No. 5,728,767 describes an aqueous resin composition comprising (a) 80 to 10 parts by weight of a modified polyolefin; and (b) 20 to 90 parts by weight of an acrylic or methacrylic monomer or mixture thereof.
U.S. Pat. No. 6,184,264 describes “switchable” adhesive compositions, which are capable of being transformed from a tacky to a non-tacky state. These compositions comprise an adhesive polymeric moiety and a plurality of bound in visible light curable groups, which are chemically bound to the adhesive polymeric moiety. The curing reaction of these adhesive compositions is initiated by visible light. This technology is also disclosed in WO 97/06836.
U.S. Pat. No. 6,262,182 describes a solution process for the modification of certain polyolefins with an unsaturated anhydride, unsaturated acid or unsaturated ester.